ArcGIS Add-In - GCD Toolbar
To install GCD Add-In for first time to ArcGIS 10.4 or later, simply double-click on downloaded *.ESRIAddin file, while NOT in an active ArcMap session. To update, remove the existing, earlier GCD 7.X add-in from your Customize → AddIn Manager menu, close ArcMap and install as per above. The video below walks you through this process of updating:
GCD Standalone
Clean Install
To install GCD 7, Standalone for the first time, simply download the latest 2018_03_28_GCDStandAlone_7_0_*.exe stand-alone executable install file from GitHub and run the application. You will need to push pass some security warnings, as shown in the video below:
Update
To update an existing installation of the GCD standalone, simply navigate to Tools → Check for Updates, if an update exists, click Yes, restart GCD, and follow prompts as illustrated in this video:
Uninstall
To unintsall the standalone GCD, simply navigate in your Windows Control Panel to Uninstall or Change Program and find GCD and uinstall it.